This invention pertains generally to multicolor electrographic printing devices. In particular, the present invention is a handling network for liquid color toners used by an electrographic printer in developing multicolor prints.
Typically, to produce a multicolor print a photoconductive member of the electrographic printer is first charged to a uniform potential to sensitize its imaging surface. The charged surface of the photoconductive member is exposed to an image of an original document that is to be reproduced as a multicolor print. This procedure allows the photoconductive member to record an electrostatic latent image corresponding to the informational areas contained within the image of the original document.
To form a multicolor print, successive images of the original document are digitally color separated and then recorded on the photoconductive member. These latent images are developed with different colored liquid toners supplied from corresponding toner developing modules of a toner handling network. The color of the liquid toner in the particular developing module corresponds to the subtractive primary of the color of the respective digitally separated image. Electrographic printing is normally done with yellow, cyan and magenta liquid toners. Usually the electrographic printer also includes a developing module having black liquid toner since it is required in virtually all commercial color printing applications.
The different colored developed images are transferred from the photoconductive member to a print medium in superimposed registration with one another. A digital half tone screen is used to expose the latent images to create multisized dots that produce the varying color tones needed to duplicate the original document. Heat is usually applied to permanently fuse the image to the print medium to form a completed multicolor print.
A liquid color toners handling network for an electrographic apparatus is disclosed in the Gross U.S. Pat. No. 3,972,610. The toner supply network of this electrographic apparatus is in the form of a closed system that includes a toner reservoir containing a supply of liquid toner. A toner pick-up tube submerged beneath the surface of the liquid toner is connected by a supply conduit to a toner pump. The pump supplies liquid toner through a first supply line to a pressure relief or bypass valve having first and second outlet ports. The first outlet of the bypass valve is coupled with the toner reservoir through a second supply line. A third supply line couples the second outlet port of the bypass valve to a toner module processing assembly.
The processing assembly includes a first solenoid valve coupled to the third supply line through a filter element. The first solenoid valve is vented to the atmosphere and has an outlet port connected to an inlet port of a second solenoid valve of the processing assembly by a short length of tube. The short tube has an internal volume corresponding to the amount of liquid toner necessary to effectuate the development of a single image.
The second solenoid valve is vented to the toner reservoir through a conduit and includes an outlet port coupled by a first fluid line to an inlet port of the toner module. An outlet port of the toner module is connected to a toner vacuum separator which separates unused liquid toner from the air and returns the separated liquid toner by gravity back to the toner fluid reservoir. A vacuum line is also connected with the toner vacuum separator and is coupled to a vacuum pump that applies a negative pressure to the vacuum separator through a regulator.
With the toner module in position to effectuate the developing process, the first solenoid valve of the toner supply network is energized which causes liquid toner to be pumped from the toner reservoir through the first solenoid valve and the short tube to the second solenoid valve. With the second solenoid valve initially in the closed position, the liquid toner is returned to the toner reservoir. This procedure allows the short tube to be filled with the precise amount of liquid toner necessary for the development of the latent image.
When the short tube is filled with liquid toner, the first solenoid valve is then closed and simultaneously therewith the second solenoid valve is opened whereupon the metered amount of toner fluid contained within the short tube is supplied to the toner module. Liquid toner is drawn through the toner module under a low vacuum supplied by the vacuum pump. This procedure causes the precisely metered amount of liquid toner to be drawn across the toner module which in turn causes the development of the latent electrostatic image. Thereafter, the second solenoid valve is closed and unused liquid toner within the vacuum separator is returned by gravity to the toner reservoir. The toner handling network does not supply liquid toner to the toner module in an "instant-on" manner. The pump must first fill the short tube and the first and second solenoid valves must be simultaneously closed and opened, respectively, before liquid toner reaches the toner module.
There is a continuing need for improved liquid color toners handling networks for electrographic printers. In particular, there is a need for a toners handling network that can supply liquid color toners to the developing modules in an "instant-on" manner to help prevent liquid toner carrying lines from drying out between imaging cycles. Moreover, there is needed a network that is capable of recirculating liquid color toner through the pumping and vacuum systems, including a simple toner drain/refill method. In addition, there is a need for a handling network that is capable of mixing liquid toner concentrate and liquid toner carrier to form the final solution of liquid color toner. There is a need for a liquid color toners handling network that includes a vacuum source for developing module maintenance, to reduce the time required to perform routine care.